Both Scatchard analysis of laminin binding studies and immunocytochemical localization of the high affinity laminin receptor using monoclonal and polyclonal antibodies have indicated that the number of laminin receptors on the cell surface may be increased in human carcinomas. Studies on human breast carcinoma-derived cell lines suggested that the increased cell surface expression of the laminin receptor was due to an increased steady state level of laminin receptor mRNA. The latter experiments suggested that assessing the laminin receptor mRNA levels of human carcinoma cells may be of diagnostic and/or prognostic value. We have developed anti-laminin receptor synthetic peptide antibodies as well as cDNA restriction fragments which are being used to assess the cell surface expression of the laminin receptor as well as laminin receptor mRNA levels in different neoplastic cell types. We evaluated the expression of laminin receptor using the immunoperoxidase technique in breast aspirates. Cells obtained from benign samples exhibited a low level of laminin receptor antigen, while 71% of smears obtained from malignant breast lesions contained cells that were strongly stained by the antibody. These data suggest that the immunodetection of laminin receptor in cells obtained by fine needle aspiration of breast lesions could be a valuable adjunct in the evaluation of breast lesions. We have analyzed paired tumor and normal tissues from individual patients with colorectal carcinoma. In each of the 18 patients studied, the neoplastic tissue contained significantly more laminin receptor mRNA than did the normal tissue. Comparable increases in laminin receptor protein were found in the carcinomatous tissue by immunoblot as well as immunohistochemical techniques. These findings suggest that increased expression of laminin receptor may be a useful marker in the evaluation of cancer patients.